The present invention relates to an image forming apparatus or an image forming method which is employed in copiers and printers.
In recent years, in image forming apparatus to obtain high image quality at a high speed, an electrostatic latent image development system such as an electrophotographic system is almost exclusively employed. It is assumed that this trend will continue into the future. Therefore, it has been increasingly demanded to further improve image quality in said electrostatic latent image development system.
In the image forming apparatus employing an electrophotographic system, known as means to remove residual toner such as non-transferred toner and residual transferred toner on the photoreceptor are, for example, cleaning units employing a blade cleaning system in which a flat board-shaped cleaning blade, comprised of an elastic body, is brought into contact with the surface of the photoreceptor so as to remove said residual toner.
Cleaning blade holding systems in such cleaning units are mainly divided into a fixed holding system in which, for example, said cleaning blade is held employing a fixed type blade holder so that said cleaning blade is brought into pressure contact with the surface of the photoreceptor utilizing the elasticity of the blade itself, and a rotary holding system in which the cleaning blade is allowed to rotate around its axis, parallel to the rotational axis of the image holding body, and said cleaning blade is brought into pressure contact with the photoreceptor employing the action of a spring force or gravity. Among them, since it is possible to stably apply constant load to the photoreceptor over an extended period of time, those employing the rotary holding system are widely employed.
However, when the cleaning blade holding system is said rotary holding system, problems tends to occur such as so-called blade curl-under.
In recent years, from the viewpoint of achieving high image quality, a decrease in toner particle diameter has been demanded. Suitably employed as methods to prepare such toner particles have been polymerization methods such as an emulsion polymerization and a suspension polymerization method.
As a method to respond to said demand for further improvement of image quality, a decrease in particle diameter of the employed toner has been undertaken. However, as the particle diameter of said toner decreases, adhesive force such as van der Waals forces between said toner and the photoreceptor (in most cases, being an electrophotographic photoreceptor) increases compared to the weight of said toner. This fact results in a decrease in transfer efficiency of said toner onto the transfer material and a decrease in cleaning efficiency. As a result, the amount of toner which is not removed on said photoreceptor increases.
However, as the toner particle diameter decreases, adhesion force between toner particles and the photoreceptor increases. As a result, it becomes increasingly difficult to remove residual toner on the photoreceptor. Specifically, a so-called polymerization toner, which is prepared employing a polymerization method, is comprised of nearly spherical particles. The resultant toner particles roll on the photoreceptor, and pass under the cleaning blade. As a result, problems occur in which insufficient cleaning or insufficient residual toner removal tends to occur, whereby it becomes increasingly difficult to remove residual toner on the photoreceptor.
Said trend is more pronounced for the toner prepared employing a so-called polymerization method which is a suitable method to prepare toner particles having a minute diameter. When an emulsion polymerization method or a suspension polymerization is employed, toner particles are directly formed. As a result, in addition to the minute particle diameter, nearly spherical toner particles are formed, whereby the effective contact area between toner particles and the photoreceptor (hereinafter occasionally referred to as the electrophotographic photoreceptor or the photoreceptor) becomes large, and further, during cleaning, toner particles tend to roll on the surface of the photoreceptor. Due to that, xe2x80x9cinsufficient cleaningxe2x80x9d occurs in which toner particles pass under the leading edge of the blade. On the other hand, in order to minimize such insufficient cleaning, when the cleaning member is excessively pressed onto the surface of the photoreceptor, the surface may be subjected to abrasion or toner particles are rubbed hard enough onto the surface to be crushed, whereby problems tend to occur on the surface of the photoreceptor. Said problems on the surface of the photoreceptor cause image problems such as white spots, white streaks, black spots, and black streaks. Accordingly, stable cleaning performance is not obtained over an extended period of time. As a result, when said problems are not overcome, it is impossible to achieve stable production of high quality images.
In order to minimize said insufficient cleaning, for example, Japanese Patent Publication Open to Public Inspection No. 3-179675 discloses a cleaning system in which mechanical cleaning and electrostatic cleaning are employed in combination.
Specifically, it is constituted in such a manner that a voltage applicable brush roller, comprised of conductive materials, is provided upstream from the cleaning blade with respect to the moving direction of the photoreceptor, and for example, a suitable bias voltage, having an opposite polarity of the residual toner on the photoreceptor, is applied to said brush roller. Thus, improvement of cleaning performance is attempted utilizing mechanical cleaning effects by the cleaning blade and electrostatic cleaning effects by the brush roller.
However, it is difficult to completely remove toner particles with a small particle diameter, and especially so are spherical toner particles which are prepared employing said polymerization method. Therefore, it has been demanded to develop a method to further enhance the cleaning performance. Further, in the image forming apparatus constituted as above, most residual toner on the photoreceptor is removed by the brush roller positioned upstream side respect to the moving direction of the photoreceptor. As a result, the amount of the residual toner, which reaches the cleaning blade, is frequently minimal. In such a case, frictional force on the photoreceptor increases so that blade curl-under as well as minute vibrations tend to occur. As a result, problems occur in which it becomes difficult to perform the stable production of high quality images over an extended period of time.
Furthermore, toner which is employed to visualize latent images formed on the photoreceptor is adhered to a wider area than the image forming area of the photoreceptor due to toner scattered by the development unit. Even though said cleaning system is employed, at present it is difficult to effectively remove the toner on the photoreceptor, which has been scattered over such a wide area.
In order to overcome such drawbacks, it has been considered to increase the cleaning area in the axis direction of the photoreceptor by increasing the width of the brush roller. However, when only the cleaning area is increased, the area, which is charged at a polarity opposite the residual toner, becomes excessively large due to the brush roller on the latent image holding member. As a result, in the opposite charge area which is charged by said brush roller and is not recharged by the charging unit, staining occurs due to toner adhesion as well as dielectric breakdown of the photosensitive layer of the photoreceptor. As a result, the apparatus interior tends to be stained and insufficient cleaning tends to occur.
Further, when the reversal development method, which is now mainly used in digital copiers, is employed, said problems are still more pronounced.
From the viewpoint of the foregoing, the present invention was achieved. An object of the present invention is to provide an image forming apparatus comprising a cleaning unit having a cleaning blade, which is capable of assuredly minimizing the formation of blade curl-under as well as minute vibrations, and is capable of producing high quality images over an extended period of time.
The other object of the present invention is to provide an image forming apparatus as well as an image forming method in which stable cleaning performance is obtained over an extended period of time and high quality images are formed without problems such as white streaks and black streaks.
Further other object of the present invention is to provide an image forming apparatus capable of assuredly removing residual toner on a photoreceptor as well as of minimizing staining in the interior of said apparatus, and subsequently capable of forming consistently high quality images over an extended period of time.
Further, another object of the present invention is to provide a cleaning unit having high cleaning performance, which results in minimized staining in the image forming apparatus in which said unit is installed.
The invention and its embodiment are described.
The image forming apparatus of the present invention comprises a rotationally driven photoreceptor and a cleaning unit which removes residual toner on said photoreceptor which has passed a transfer zone in which a toner image formed on said photoreceptor is transferred to a recording material in which
said cleaning unit comprises a cleaning roller which is disposed so as to come into contact with the surface of said photoreceptor, a bias voltage applying means which applies a bias voltage to said cleaning roller, and a flat board-shaped cleaning blade comprised of an elastic body which is disposed so that the leading edge of said cleaning blade comes into contact with the surface of said latent image holding member downstream from said cleaning roller with respect to the movement direction of said photoreceptor, and
said cleaning blade is supported rotatably around predetermined rotationally driven center axis O parallel to the rotational axis of said photoreceptor so that said cleaning blade is rotationally driven from the standard state in which the leading edge comes into contact with the surface of said photoreceptor while its total shape is not deformed and subsequently, is subjected to a working state while its entire body is curved, and
the position of said rotationally driven center axis O is set so that said cleaning blade, in its standard state, satisfies the Conditions (1) and (2) described below:
Condition (1): in the cross-section perpendicular to the rotational axis of said photoreceptor, straight line T drawn between contact position P of the leading edge of said cleaning blade with said photoreceptor and said rotationally driven center axis O is positioned between tangential line N at said contact position P and said cleaning blade, and
Condition (2): in the cross-section perpendicular to the rotational axis of said photoreceptor, contact angle xcex8 of said cleaning blade with respect to the tangential line of said photoreceptor at said contact point P is from 0 to 30 degrees.
In the image forming apparatus of the present invention, the contact load on said cleaning blade is preferably from 5 to 50 g/cm.
Further, said bias voltage applying means is a constant current power source.
Still further, toner employed to form said toner image may be comprised of toner particles having a volume average particle diameter of 8.5 xcexcm or less, which are prepared employing a polymerization method.
The image forming apparatus of the present invention comprises a rotationally driven photoreceptor, an image forming unit which forms a toner image on said photoreceptor employing toner comprising a lubricant as the external agent, a transfer unit which transfers said toner image formed employing said image forming unit onto a recording material in the transfer zone, and a cleaning unit which removes residual toner on said photoreceptor which has passed said transfer zone, wherein
said cleaning unit comprises a cleaning roller which is disposed so as to come into contact with the surface of said photoreceptor, a bias voltage applying means which applies a bias voltage to said cleaning roller, and a flat board-shaped cleaning blade comprised of an elastic body which is disposed so that the leading edge of said cleaning blade comes into contact with the surface of said latent image holding member downstream from said cleaning roller with respect to the movement direction of said photoreceptor, and
which comprises a control mechanism comprising a specified toner image forming function which forms a toner image for maintaining a blade effect to maintain the desired cleaning effect of said cleaning blade which reaches a cleaning zone employing said blade after passing said transfer zone.
In the image forming apparatus of the present invention, said control mechanism is capable of allowing said toner image for maintaining a blade effect to reach said cleaning zone, in which said cleaning blade is employed, by decreasing the cleaning effect obtained by said cleaning roller. In this case, when said toner image for maintaining the blade effect passes the cleaning zone in which said cleaning roller is employed, it is preferable that the cleaning effect obtained employing said cleaning roller is decreased by decreasing or eliminating the bias voltage which is applied to said cleaning roller.
In said image forming apparatus, it is possible to constitute it in such a manner that the specified toner image forming function of said control mechanism controls the operation of said image forming unit so that said toner image for maintaining the blade effect is formed at every specified image forming frequency.
Further, said bias voltage applying means is comprised of a constant current power source.
Still further, said toner employed to form a toner image may be comprised of toner particles, having a volume average particle diameter of 8.5 xcexcm or less, which are prepared employing a polymerization method.
The image forming apparatus of the present invention comprising a photoreceptor which is rotationally driven, a charging unit which is arranged so as to face said photoreceptor while maintaining parallel to the axis, and charges said photoreceptor, a development unit which visualizes the latent image on said photoreceptor employing a toner, a transfer unit which is arranged to face said photoreceptor while maintaining parallel to the axis and transfers a toner image on said photoreceptor onto a recording material in the transfer zone, and a cleaning unit which removes the toner on said photoreceptor which passes through said transfer zone,
in which said cleaning unit comprises a cleaning blade which comes into contact with the surface of said photoreceptor, a cleaning roller which comes into contact with the surface of said latent image holding member upstream with respect to the movement direction of said photoreceptor and is arranged to maintain parallel to the axis of said photoreceptor, and a bias voltage applying means which applies a bias voltage to said cleaning roller,
is characterized in that formulas (1) and (2) described below are satisfied;
W2 less than W1xe2x80x83xe2x80x83Formula (1)
|W3xe2x88x92W1|xe2x89xa630 (in mm)xe2x80x83xe2x80x83Formula (2)
wherein W1 is the effective cleaning area obtained by said cleaning roller in the axis direction of said photoreceptor, W2 is the effective transferring area of said transfer unit, and W3 is the effective charging area of said charging unit.
In the image forming apparatus of the present invention, it is preferable that the bias voltage applying means in said cleaning unit is a constant current power source.
Further, in said image forming apparatus, toner which is employed to visualize a latent image may be comprised of toner particles having a volume average particle diameter of 8.5 xcexcm or less, which is prepared employing a polymerization method and further may be comprised of toner particles having a volume average particle diameter in the range of 2 to 32 xcexcm, which have a CV value of no more than 20 percent.
Still further, in said image forming apparatus, the development unit may be constituted so that latent images formed on the photoreceptor are visualized employing a reversal development method.
The image forming apparatus of the present invention comprising a photoreceptor which is rotationally driven, a charging unit which is arranged to face said photoreceptor while maintaining parallel to the axis and charges said photoreceptor, a development unit which visualizes the latent image on said photoreceptor employing a toner, a transfer unit which is arranged to face said photoreceptor while maintaining parallel to the axis and transfers a toner image on said photoreceptor onto a recording material in the transfer zone, and a cleaning unit which removes the toner on said photoreceptor which passes through said transfer zone, in which said cleaning unit comprises a cleaning blade which comes into contact with the surface of said photoreceptor, a cleaning roller which comes into contact with the surface of said latent image holding member upstream with respect to the movement direction of said photoreceptor and is arranged to maintain parallel to the axis of said photoreceptor, and a bias voltage applying means which applies a bias voltage to said cleaning roller,
is characterized in that said cleaning roller is insulated in its lateral direction in the part which is located beyond the part corresponding to the area effectively charged by said charging unit.
In said image forming apparatus, it is preferable that the bias voltage applying means in said cleaning unit is a constant current power source.
Further, in said image forming apparatus, toner which is employed to visualize a latent image may be comprised of toner particles having a volume average particle diameter of 8.5 xcexcm or less, which are prepared employing a polymerization method. Further, the development unit may be constituted so that latent images formed on the photoreceptor are visualized employing a reversal development method.
The cleaning unit of the present invention comprising a cleaning blade which comes into contact with the surface of said rotationally driven latent image holding member, a cleaning roller which is arranged to come into contact with the surface of said photoreceptor upstream with respect to the movement direction of said latent image holding member from said cleaning position and to maintain parallel to the axis of said photoreceptor, and a bias voltage applying means which applies a bias voltage to said cleaning roller,
is characterized in that said cleaning roller is conductive in its lateral direction in the part corresponding to the area in which the surface of said photoreceptor is effectively charged by said charging unit and is simultaneously insulated in the part beyond both edges of the part corresponding to said effectively charged area.
In one of the embodiments cleaning means comprises
a cleaning roller comprised of an conductive or semi-conductive elastic body,
a cleaning blade which is provided on the downstream side of said photoreceptor movement direction from said cleaning roller so as to come into contact with the surface of said photoreceptor,
a constant current power source which applies a bias voltage having a polarity opposite the charging polarity of the toner which has contributed to the formation of said toner image in development utilizing said development means, and
a removal means which removes any residual toner from said cleaning roller, and
surface roughness Rz of said photoreceptor is from 0.1 to 2.5 xcexcm.
The constant current power source outputs a constant current of 1 to 50 xcexcA.